AB0199 THE PROGNOSTIC VALUE OF IGA ANTI-CITRULLINATED PROTEIN ANTIBODY AND RHEUMATOID FACTOR IN AN EARLY ARTHRITIS COHORT WITH A TREAT-TO-TARGET APPROACH
Authors: J. Heutz, M. W. Schreurs, A. Van der Helm – van Mil, P. De Jong
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> The EULAR research agenda states that new biomarkers are needed to stratify patients and to predict therapeutic response or lack of response in rheumatoid arthritis. Currently, IgG anti-citrullinated protein antibody (ACPA) and IgM rheumatoid factor (RF) are used as poor prognostic factors for treatment decisions in RA. The mucosal origin hypothesis of RA renewed the interest in the role of IgA isotype autoantibodies for disease pathogenesis. However, the value of IgA ACPA and RF for prognostication of treatment response under a treat-to-target approach is not clear to date. <h3>Objectives</h3> To evaluate the prognostic value of IgA ACPA and RF by considering 'quick-attained and persistent remission', DMARD-free remission (DFR) and biological use in an early (rheumatoid) arthritis population. <h3>Methods</h3> All patients from the treatment in the Rotterdam Early Arthritis Cohort (tREACH) trial with available baseline sera were included. The tREACH trial is a multicentre, stratified, single-blinded trial with a treat-to-target approach. IgA ACPA and RF isotypes were measured by automated fluorescence enzyme-immuno assay (FEIA) in baseline sera. The prognostic value of positivity for IgA ACPA and RF was evaluated for three outcome measures: (1) quick-attained (at 6 months) and persistent (to 2 years) remission, analysed with logistic regression analysis; (2) achievement of DFR for at least 6 months over a 2 year follow-up period, analysed with survival analysis; and (3) incident biological use over 2 years, analysed with mixed effects logistic regression analysis. Results were stratified for IgG ACPA, since it is known that IgG ACPA is related to lower (DMARD-free) remission rates and more biological use. <h3>Results</h3> IgA isotypes of ACPA and RF were measured in baseline sera of 480 tREACH patients. 66% was female, mean age was 53 years, median symptom duration 21 weeks, and median swollen joint count 5. A positive IgA ACPA titre was present in 109 (23%) patients and most of them also had a IgG ACPA result above the cut-off value for positivity (n=102, overlap of 94%). Positive IgA RF on the other hand was present in 172 (36%) of patients, which overlapped with IgM RF for 90% (n=154). Double positivity for IgA and IgG ACPA (n=102) revealed lower DFR rates after 2 years compared to IgG ACPA positivity alone (6% and 11%, respectively, Figure 1A), although this finding was not significant (p=0.09). No differences were observed in 'quick-attained and persistent remission' and biological use for both IgA ACPA and RF, after stratification for IgG ACPA. <h3>Conclusion</h3> IgA isotypes of ACPA and RF almost completely overlap with the commonly measured isotypes (IgG ACPA and IgM RF, respectively). In addition, both an IgA ACPA and IgA RF response do not predict persistent remission, DFR and biological use in this treat-to-target population. Based on these results, there is no rationale for measuring these isotypes in newly diagnosed (rheumatoid) arthritis patients in daily clinical practice. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.